In the Garden:Pacific Northwest
February, 2005
Regional Report

Highly adaptable, this Houttuynia is as happy growing in a sunny pond as it is in a dry, shady bed. If allowed, it will gleefully take over any spot in the garden.

Taming Ill-Mannered Plants

I like to do a little research before bringing a plant home from the nursery. It's not that I'm being snobbish; I just don't want to unwittingly contribute to my neighborhood's collection of invasive plants.

Scotch broom, purple loosestrife and Japanese knotweed have all escaped cultivation here in the Pacific Northwest, and can be seen covering hillsides, choking lakes, and crowding out native understory in forested areas. At one time these plants were readily cultivated, considered welcome additions to local gardens. Little did we know how invasive these plants could become or what long-range problems they would cause.

My first experience with a strong-willed plant was with Houttuynia cordata 'Chameleon', an innocent-looking little snippet with heart-shaped, tri-colored leaves and small white flowers. Sold as a ground cover, this lovely little plant has a tenacious personality. Quietly working underground, it popped up where I least expected -- 10 feet from the original bed!

I chose this plant for an especially difficult spot in my garden because it grows in wet or dry soils in shade or sun, is not attractive to slugs, and has no particular insect or disease problems. Well, if it sounds too good to be true, there's got to be a catch. My new Houttuynia behaved as promised and then some! Now that I'm more familiar with its wanderlust ways, I'm prepared to keep it in line by anticipating its escape from the bed. This plant is especially easy to contain. All I do is pull it out, snake-like rhizomes and all. Unfortunately, not all plants with aggressive characteristics are quite so easy to manage.

Controlling Overzealous Plants
Most ill-mannered plants are attractive, making them hard to resist, but I now realize that descriptions such as "grows in poor or average soils," "drought-resistant," "makes a great ground cover" or "is a low-maintenance plant" are actually tip-offs that they are potentially invasive. These warnings may not prevent me from planting a specific plant, but I'll make a note of it and watch the plant carefully. If you choose to plant something with a questionable reputation, you can try these steps to control a plant's unacceptable behavior.

Deadhead. Remove all flower heads as they fade to limit the offspring of many would-be parent plants. Coneflower (Echinacea) and black-eyed Susan (Rudbeckia hirta) can produce thousands of seeds in a season. Pulling out or hoeing seedlings, in combination with deadheading, will usually control the majority of rampant self-seeders, including yarrow, lambs' ears (Stachys byzantina) and spurge.

Don't Spoil Them. Most pervasive plants do well in poor soil with little maintenance, but if you pamper plants such as spurge or evening primrose (Oenothera spp.) with more water and fertilizer, they can become invasive.

Pull, Pull, Pull. The only way to control some plants is to physically pull out new shoots, roots and all. Although it can be hard work, relentless pulling will eventually eliminate even the most persistent of plants. This is effective for controlling lambs' ears, dame's rocket (Hesperis matronalis), mint, common violets, and English ivy (Hedera helix).

Mulch. A thick mulch will prevent seeds from touching bare soil and taking root. If you cover the ground with a 3- to 4-inch layer of organic material, such as hay, straw, grass clippings, or wood chips, any seeds that germinate will be simple to pull, roots and all.

Relocate. Find a place in your garden where a plant's rampant tendencies can be an asset. Evening primrose, snow-in-summer (Cerastium tomentosum) and spotted deadnettle may be too aggressive for the perennial border but just right for a hot or dry area where little else will survive.

Contain Their Roots. Some plants should be grown in pots to contain their roots; herbs such as mint, thyme and marjoram are good examples. To control horizontal spreading of creeping plants, plant them in bottomless (for good drainage) containers sunk into the ground up to rim level.

An Ounce of Prevention
Even the most innocent-looking plants can have bad habits. Before bringing a new plant home from the nursery, it pays to ask a few questions: Does it stay where it is planted or does it like to wander? Will it pop up in unexpected places because birds or wind spread its seeds? Will it creep, climb, or otherwise terrorize more civilized plants in your garden? If so, do you want the responsibility of keeping it under control or should you choose another plant instead?

Finally, before accepting a gift from someone else's garden, keep in mind that if they have too many of whatever it is, chances are before long, you will too.